ENS Connection Pooling

The connection pooling feature of ENS enables a pool of subscribers
to receive notifications from a single event reference. For every event, ENS
chooses one subscriber from the pool to send the notification to. Thus, only
one subscriber in the pool receives the notification. The ENS server balances
sending of notifications among the subscribers. This enables the client to
have a pool of subscribers that work together to receive all notifications
from a single event reference.

For example, if notifications are being published to the event reference enp://127.0.0.1/store, a subscriber will normally subscribe to this
event reference to receive notifications. To have a pool of subscribers receive
all the notifications to this event reference, each subscriber in the pool
only needs to subscribe to the event reference enp+pool://127.0.0.1/store instead. The ENS server chooses one subscriber from the pool to
send the notification to.

Note –

The publisher still sends notifications to the simple event reference,
in the example above enp://127.0.0.1/store, that is, the
publisher has no knowledge of the subscriber pool.

Multiple Pool Extension

Connection pooling can support multiple pools of subscribers. That is,
you can have two pools of subscribers, each pool receiving all the notifications
from the event reference. The syntax of the event reference for the subscriber
is:

enp+pool[.poolid]://domain/event

where poolid is a string using only base64
alphabet. (See RFC1521, Table 1, for what the base64 alphabet contains.) So,
for example, to have two pools of subscribers to the event reference enp://127.0.0.1/store, each pool could subscribe to the following event references:

enp+pool.1://127.0.0.1/store– for first pool
of subscribers enp+pool.2://127.0.0.1/store– for
second pool of subscribers